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By: Imed Dami and Diane Kinney, Horticulture & Crop Science, The Ohio State University
This article summarizes the 2020 dormant and growing seasons and the impact of weather on grape varieties grown on the research vineyard at the OSU-OARDC in Wooster, Ohio.
2020 was a very different year from its very beginning. The first quarter of the year was unusually warm with mean January temperatures in the 30s. At our research vineyard, the lowest recorded winter temperature was 3.7 °F, which occurred on February 15th. However, the temperature trend was reversed during the second quarter, with both April and most of May having cooler temperatures than normal. A statewide frost event occurred the week of April 12th; temperatures dropped to 24.6 °F in Wooster on April 16th. We were fortunate to receive little injury as we had no budbreak at this time, but another drop in temperature to 29 °F on May 9th caused small amounts of injury to some primary shoots. June temperatures leveled out, but July temperatures were above normal and over 90 °F daytime maximum temperatures for 8 days. During the ripening period of August through October, temperatures were very moderate and on track with the long-term average. The killing frost occurred on November 13th. Both months of November and December followed the 2019 trend of being warmer than normal by 3-4 6 °F.
The 2020 precipitation changed drastically from the previous two seasons. The 2020 cumulative precipitation was only 34.24” (2.66” over the long term) vs. the very wet 2018 (44.5”) and 2019 (44.1”). Although we started off gaining over 8.9” by the end of March, July was very dry (more than 2” below the long-term average). Precipitation during ripening was a bit over normal but not excessive. Discounting rainfall from late winter/early spring, the season ended with below-normal precipitation.
2020 Spring freeze injury: We were fortunate to escape the winter months without winter injury. Thanks to a cool April, which slowed down budbreak, the April 16th freeze did not affect us in Wooster since grapevines had not broken bud at that time. After the May 9th temperature drop, we did observe a small amount of freeze damage to the earliest budbreak varieties, but not much due to the late bud break. The cool weather actually may have helped us during the COVID-19 restrictions and later than normal pruning practices.
Diseases and insects: For the most part, fruit remained clean throughout the growing and ripening season. There was some concern for berry shrivel during the drought months of July and early August but that was quickly remedied with ample rain following hurricane Laura. Timing harvest with small amounts of rain occurring resulted in sour rot in some susceptible varieties. We also observed significant bee and bird pressure in early September that likely contributed to sour rot development. As always, the Japanese beetles made their presence known but only small amounts of defoliation occurred when coupled with timely insecticide sprays in the vineyard.
Fruit quality: Our harvest season came fast and furious between the dates of September 1st and October 7th. Overall, yields were low for two reasons: newly established vines were still recovering from the winter injury in 2019; and the negative impact of the spring frost in May 2020. As shown in the table and figures below, sugars were lower and acids were higher than in previous years. This is likely related to the lower mean temperatures and GDDs than those in 2018 and 2019 during ripening. Nevertheless, based on tasting of berry juice at harvest, fruit flavors developed nicely and were characteristic of most red and white varieties.
2020 Harvest fruit composition of selected grape varieties at the Wooster research vineyard: